1. Field of the Invention
The present invention relates to an active element such as a transistor formed over a large-sized glass substrate, a liquid crystal display device (hereinafter also referred to as a “LCD”) and an EL display device containing the active element, and a manufacturing method thereof. Particularly, the invention relates to a thin film transistor, a liquid crystal display device, and an EL display device using a droplet discharging method typified by an ink-jet method, and a manufacturing method thereof.
2. Description of the Related Art
Conventionally, a so-called active matrix driving liquid crystal display panel including a thin film transistor (hereinafter also referred to as a “TFT”) over a glass substrate has been manufactured by patterning various thin films according to a light-exposure step using a photomask in the same manner as a manufacturing technique of a semiconductor integrated circuit.
A manufacturing technique to carry out mass production efficiently has been employed up to now by dividing one mother glass substrate into a plurality of liquid crystal display panels. The mother glass substrate has enlarged from a size of 300 mm×400 mm of the first generation at the beginning of the 1990s to a size of 680 mm×880 mm or 730 mm×920 mm of the fourth generation in 2000; thus, the manufacturing technique has developed so that a number of display panels can be obtained from one substrate.
When the size of a glass substrate or a display panel is small, patterning treatment can be performed comparatively easily by using a photolithography apparatus. However, an entire surface of a display panel cannot be simultaneously treated by performing light-exposure treatment once as a substrate becomes larger. Consequently, a method or the like for dividing a region where a photoresist is coated into a plurality of regions, performing light-exposure treatment on every predetermined block regions, and exposing an entire surface of a substrate to light by sequentially repeating the treatment has been developed (for example, see Reference 1, Japanese Patent Laid Open No. H11-326951).
In addition, a technique to provide a comparatively low-concentration impurity region (LDD region: Lightly Doped Drain region) formed at the ends of a source and/or drain region in order to relax an electric field concentrated at the ends of the drain regions of a plurality of TFTs and to suppress a so-called hot carrier (hot electron or hot hole) effect is used when an active matrix substrate including the plurality of TFTs which is used for an active matrix LCD or an EL display device is formed (for example, see Reference 2, Japanese Patent Laid Open No. H10-135468).
However, a glass substrate is further enlarged to a size of 1000 mm×1200 mm or 1100 mm×1300 mm in the fifth generation, a size of 1500 mm×1800 mm in the sixth generation, a size of 2000 mm×2200 mm in the seventh generation, and a size of 2500 mm×3000 mm or more is assumed in the eighth generation. It is difficult to manufacture a display panel with good productivity with low cost only by a conventional patterning method. In other words, when a plurality of times of light-exposure is performed by consecutive light exposure, a processing time is increased and it is difficult to handle large substrates.
In addition, in the case of providing an LDD region for a TFT, it is necessary to form separately an insulating film to be a mask or to contrive the shape of a gate electrode layer in order to have the concentration difference in impurities injected in a semiconductor film; therefore, the number of patterning steps has increased as a matter of course and the step has become complicated. As the number of the steps increases, naturally, the cost for running an apparatus and the material cost run up, and there is a problem that a large amount of waste solution containing heavy metal, insulator, or the like is required to be disposed.